Organic Tandem Solar Cells with 15% Efficiency Employing Novel Wide Bandgap Nonfullerene Acceptor
Yuliar Firdaus a, Qiao He b, Yuanbao Lin a, Ferry Anggoro Ardy Nugroho c, Emre Yengel a, Ahmed H. Balawi a, Frederic Laquai a, Christoph Langhammer c, Feng Liu d, Martin Heeney b, Thomas D. Anthopoulos a
a King Abdullah University of Science and Technology (KAUST) - Saudi Arabia, 4700 King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
b Department of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London, United Kingdom
c Chalmers University of Technology, Sweden, Fysikgränd, 3, Gothenburg, Sweden
d Shanghai Jiao Tong University, CN
Oral, Yuliar Firdaus, presentation 043
Publication date: 14th October 2019

Fabricating solar cells with tandem structure is an effective way for increasing the power conversion efficiency (PCE) beyond that of single-junction organic photovoltaics (OPV). To obtain high PCE of the tandem OPV, carefully engineered front-cell and back-cell are required. However, wide-bandgap materials for front cells that have both high short-circuit current density (JSC) and open-circuit voltage (VOC) are scarce. In this contribution, we developed and studied two new acceptor molecules namely IDTA and IDTTA with optical bandgaps (Egopt) of 1.90 and 1.75 eV, respectively. When blended with wide bandgap polymer PBDB-T, single-junction cells with PCE up to 7.4% for IDTA and 10.8% for IDTTA (with high VOC = 0.98 V, JSC = 15.8 mAcm-2, and FF = 70%) are demonstrated. The latter PCE value is the highest reported to date for wide-bandgap (Egopt ≥ 1.7 eV) OPVs. Our detailed transport and recombination studies show that the improved charge transport in IDTTA-based cells leads to higher fill-factor and improved charge generation than IDTA-based devices. Moreover, IDTTA-based OPVs show improved shelf lifetime and thermal stability. Nanoplasmonic spectroscopy analysis reveals that the PBDB-T:IDTTA layer exhibits significantly higher glass transition temperature, which could explain its superior thermal stability at 80°C. Finally, with the aid of optical-electrical device simulation, we were able to combine PBDB-T:IDTTA as the front-cell with PTB7-Th:IEICO-4F as the back-cell in tandem OPVs and demonstrate cells with PCE = 15%, open circuit voltage of 1.66 V and short circuit current of 13.6 mA/cm2; in good agreement with our theoretical predictions. These results highlight IDTTA as a promising acceptor for high performance tandem OPVs.

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